Spring counterbalance for drafting machines



-Novf 7, 1944- R. H. COLE ET AL. 2,362,050

SPRING COUNTERBALANCE FOR DRAFTING MACHINES Filed Sept. 16, 1941 2 Sheets-Sheet l lnnnnninnglp 5?/ RUSSELL 60.45,

' 'I PERRY Q01/ER 57.2'6. 3 INVENTOR/ I Nov. 7, 1944.

R. H. COLE ETAL SPRING COUNTERBALANCE FOR DRAFTING MACHINES Filed Sept. 16, 1941 2 Sheets-Sheet 2 Az/ssfu H. CoLE, Hmm GL01/5R,

- INVENTOR TOR Patented Nov. 7, 1944 SPRING COUNTERBALANCE Fon n RAFfrI-NG MACHINES Russell H. Cole., San. Gabriel,and1*errx E Glover* Pasadena Calin assignorsr by memo assignv ments, to. Vard, Ivnc., Pasadll'a, Calif. @Qli-A poration of r(Qjalifornia Application September 16, 194.1, Serial No.` 410,996

s claims.. (ci, sofia),

Our invention relates to drafting machines and has particular reference to a spring counterbalance device adapted to counterbalance thew-eight of the drafting machine head and parallel motion mechanism on which the head is carried, the

device finding particular utility when employed Atu use of spring counterbalancing systemsl have not been Aentirely successful. TheA spring counterbalance used prior to our invention either sub- 'stituted a spring -for the weight employed in the older counterweight systems and so were characterized bythe same disadvantages or ernployed a spring connected betweena fixed anchor and one of the arms or the Ilexibl'e band' of' the parallel motion mechanism. Suche. connection tended to impair the accuracy with Which the l parallel 'motion mechanism guided the mover Ya Aspring counterbalancefor drafting machines which includes a spring device tending normally to overcome the tendency'of the parallel moticmr mechanism to swing downwardly' about vthe an- Chor pivot.

It' is a Still further object of:v our invention to provide a device of the character set forth in the preceding paragraph inwhichV the vspring isv associated with the anchorand operates independently of the flexible bands 'of the parallel motion mechanismto provide the desired coun-V terbalancing'torque.

Itis, an. additional object' of our invention to l inFlgql a rdrafting machineo'f the endless band type as being employed upon a drawing board provide a device of the" character set forth in the precedingy paragraphs in which-a spring pressed member is' positioned to engage a cam, the spring pressed member 'and the cambeing moved relative to each other bymovement of the parallel motion mechanism about its fixed anchor.

1t is also an object of our invention to provide a devi-ce o f the character set forth hereinbefore which, includes af simple and readily operable mechanism for adjusting the magnitude of the counterbalancingtorque produced, thereby providing for the ready adaptation of the device to drawing boards of different inclinations.

Other objects and advantages of our invention will be apparent from a study of the following specification, `read in connection with the accompanying drawings, wherein:

Fig. lis aplanview illustrating a drafting machine employing a `parallel mot-ion mechanism of the endless band type, the machine shown in Fig; 1 being provided with a spring counterbalancing device constructed in accordance with the preferred embodiment of our invention; v

Fig. is ia vertical sectional View taken substantially along the line Il--H of Fig. 1 to illustrate. the detailsof constructiony of the counterbaiancing device Fig.r 3' is a horizontal sectional view taken substantially along the line III-III of Fig. 2 toillustrateA additional details; of, construction andillustratin'g' also; by" means of dotted lines, the Inanner in which-the device operates to produce the desired counterbalancing torque;

Fig. 4 is a sectional view'similar tov Fig. 2 but illustrating the construction of aY modified'form ofourinventionjsand Fig` 5' is a horizontal sectional view taken substantially along theline V-V of Fig. 4 to illustrate additional details ofl construction and illustrat-ing' MSO., by means'of dotted lines, the manner inwhichthedevice operates.

- Referring to the drawings, We have illustrated or drawing table I. The drafting machine includes a drafting machine head 2 adapted to support rulers or scales 3 andjlj. The head-2` is mounted fory freet-ranslatory movement' over the surfaceoff the board l tol permit the scales 3 andi 4` to be. positioned as desiredon the board. The headv 2 is supported fromV aparallel motion mechanism which includes interconnected? 'frointed` arms 5 and 6", the headk Z-being supported upon one end ofthel armfwhile ,the freefendtof the' arm 5` yis pvdtallyl secured?l tol the upper edge of the drawing board I as by means of an anchor clamp l. The jointed arms and 6 also include a parallel motion mechanism which operates to maintain the angular position of the scales 3 and 4 relative to the drawing board I constant irrespective of movement of the head 2 over the surface of the board.

The parallel motion mechanism illustrated in Fig. 1- comprises the well known flexible band and pulley type, this mechanism including a fixed pulley 8 associated with the anchor I and about which a iiexible band 9 is passed. The band 9 alsok encircles an elbow pulley enclosed and pivotally supported within the elbow housing il), this pulley engaging also a second flexible band which surrounds a pulley enclosed within the housing I2 associated with the head 2 and fixed to such head. The interconnection of the bands 9 and II by virtue of the elbow pulley causes the l head 2 to maintain a Xed angular position irrespective of pivotal movement of the` arms 5 and 6 about the anchor I and about the elbow IIJ.

Ordinarily in using drafting machines such as that illustrated in Fig. 1, it is desirable for convenience in drafting work to incline vthe drawing board I at a slight angle (up to 15 or 20), the upper edge of the board to which the anchor 'I is secured being disposed at a higher elevation than is the opposite edge of the board. When the board is thus inclined, the weight of the scales 3 and 4, the head 2 and the parallel motion mechanism tends to continually cause the drafting machine to swing downwardly about the anchor I. The preferred embodiment of our invention includes a spring eounterbalancing means associated 4with the anchor 'I and tending to normally resist this tendency of the drafting machine to swing about the anchor pivot. The anchor clamp 1 is best illustrated in Fig. 2 and includes a means for xedly securing the clamp to the edge of the board I and supports a xed upwardly extending pivot shaft I3. Upon this shaft the pulley 8 is secured, the same being enclosed by a housing mounted upon the shaft I3 as by means of suitable bearings I5 and I6. The housing I4 includes a neck-like extension l1 into which the end of the arm 5 is secured.

The spring counterbalancing device includesy a cam member I8 which, in the form illustrated in Fig. 2, is secured to the' anchor clamp 1 as by means of suitable clamping screws I9. The periphery of the cam member I8 is engaged by a spring pressed member 20 which is slidably supported within a tubular housing 2l secured to or preferably formed integrally with the neck portion I'I and disposed on the underside of such portion. Within the housing 2| is positioned a compression spring 22, one end of the spring 22 bearing against the innermost end of the memlber 20 and the opposite end of the spring 22 being engaged by the inner end of an adjusting screw 23, the screw 23 being adjustably movable axially of the housing 2| by virtue of a threaded engagement therewith afforded by external threads 24 formed on the member 23 and internal threads 25 formed on the 'interior of the housing 2|. The spring 22 may be held centralized in the housing 2| by providing an inwardly projecting stub 26 on the adjusting member 23.

Friction resulting from the engagement of the member 20 with the periphery of the cam I8 may of the member 20 to dene a pair of arms 21 and I4 which is pivotally.

28 between which is positioned a small roller 29, the same being supported upon a suitable axle or pivot shaft 30 extended between the arms 2'I and 28. When such a construction is employed it is necessary that the member 20 be held against pivotal movement about the axis of the housing 2| while being permitted sliding movement axiallythereof. For this purpose a keyway 3| is formed in one side of the member 20 and a small screw or pin 32 is secured to the housing 2U in a position t0 extend into the key- It will be noted that as the arm 5 is pivotally moved about the axis of the anchor shaft I3, the spring pressed member 20 will be moved about the periphery of the cam member I8. As is clearly illustrated in Fig. 3, the cam member I8 is preferably of circular form, being disposed eccentrically with respect to the shaft I3. Thus, as the arm 5 is moved about the pivot I3 in such manner as tc move the housing 2| .from the position illustrated in solid lines in Fig. 3 to the position illustrated in dotted lines in that figure, the distance between the point of engagement of the spring pressed member with the surface of the cam and the axis of the pivot shaft I3 will change, thus causing the member 20 to be moved inwardly or outwardly in the housing 2| either against the force of the spring 22 or in the direction of the force of the spring, depending upon the direction of movement of the arm 5.

Preferably the cam member I8 is so positioned that the point of greatest radius, identified by reference character 33 in Fig. 3, lies directly below the center of the anchor shaft I3. When the parts are thus positioned, movement of the spring pressed member 20 from the position illustrated in solid lines in Fig. 3 to the position illustrated in dotted lines in that ligure will cause the member 2|) to be moved inwardly into the housing 2| against the force of the spring 22. Thus the spring 22 provides a counterbalancing. torque tending to resist this movement of the arm 5. The magnitude of this counterbalancing torque may be adjusted at will by screwing the adjusting member 23 inwardly or outwardly of the housing 2| to further compress the spring 22 or to reduce the pressure exerted thereon. Thus the counterbalancing force developed by the spring 22 may be adjusted to suit the particular inclination of the drawing board I.

It will be noted that if the arm 5 is pivotally moved a distance sufficient to shift the spring pressed member 2|! to the opposite side of the point 33 from that illustrated in Fig. 3, the direction of the counterbalancing torque will be reversed so that instead of tending to produce a counter-clockwise movement of the device the spring will now tend toproduce a clockwise movement of the device. As hereinbefore stated, the illustrated location of the point 33 is preferred. However, under certain circumstances it may be desired to position the point 33 other than as illustrated and our invention contemplates mounting the cam member I8 upon the anchor member 'I in an adjustable manner as by providing suitable arcuate slots 33a in the cam member I8 so that the point 33 may be positioned as desired to suit particular or unusual drafting requirements.

iAttention is directed to the fact that by pro-` viding the cam I8 with a circular form, the magnitude of the restoring torque varies with the position of the arm 5. This is an advantage for' the reason that the torque produced by the weight ofv the drafting machine and tending to cause the same to swing about the anchor 1 also varies with the position of the arm 5. It may, however, be desirable to employ a cam la of a 4form other'than circular, andr it is within the vice. the cam member identined byreference character We secured te, the, pulley housing .14 se as to` be, rotatable by pivotal movement of the arm 5i about the anchor pivot shaft I3., Similarthe spring pressed device identied by referense character u slidably` supported Within a .housing-Md which; is-secured. to, or formed ,in--

tegrally with; the anchor 1,.

It will be notedthat in both forms. of the in vention, pivotalk movement of thearm ,5. about i the. Shat [-3 causes relative movement between the spring presse@ member and the peripheral sur-face, of the cam member. Thedevice illustrated in ligs.4 4 and operates in, precisely the same manner as. has. been previously described in connection with the preferred` form of our invention to providey av counterbalancing torque which will prevent the drafting machine from swinging.` about its anchor as a result of the in,- clination of .the drawing board.

In the form illustrated in Figs. 4 and 5 an al ternative constructiony of the housing 2 la isillustrated. It willA be noted that the housing 2| a is somewhat shorter than the housing 2 I^ previously described, this shortening being obtained by forming the adjusting member 23a with an axial counterbore 34 in which the compression spring 22a is seated;

It willbe noted that we have provided' a spring counterbalancing for drafting machines which is associated with the anchor end of the parallel motion mechanism.

It will also be noted that the device is small and com-pact andf is of simple construction permitting it to be readily and speedily manufactured at low oost,

Attention is directed to the fact that the counterbalancing torque produced by the device is applied to the jointed arms 5 and 6 independently of the parallel motion mechanism comprising the endless bands 9 and Il and the associated pulleys. Thus the device does not tend to produce any unusual or unbalanced loads upon the device and so does not cause undue or rapid wear of the various parts of the drafting machine.

The provision of the adjusting members 23 and 23a permits the magnitude of the counterbalancing torque to be readily adjusted, thereby adapting the device for use on drawing boards of different or varying inclinations.

While we have shown and, described the preferred embodiment of our invention, we do not desire to be limited to any of the details of construction shown or described herein, except as defined in the appended claims.

We claim:

1. In a spring counterbalance for a drafting machine including an anchor member defining a fixed axis pivotally supporting an arm memberi of a parallel motion mechanism, the combination of: a cam secured to one of said members and dening a cam surface eccentrically disposed relative to said fixed axis; means on the other of said members defining a tubular housing directed toward said cam surface; a cam engaging element slidably mounted in said housing and extending out of one `end thereof to engage said cam surface;v closure means closing the other end of said housing; and compressionV spring means conned in said housing between said element and said closure means for forcing said elfement into engagement with said cam surface,

. said closure means being threadedly engaged with said housing whereby rotation of said closure means adjustsl the force exerted by said compres;-

sion spring means. f

2. In a spring counterbalance. for a drafting machine including an anchor member defining a iixed axis pivotally supporting an:v arm member of a parallel motion mechanism, the combination of: a cam secured to one. of said members and defining a cylindrical camy surface extending about said fixed axis with the axis of' said surface disposed parallel to and offset from said fixed axis.; meansV on the other of said members dening a tubular housing directed toward said cam surface; a cam engaging element4 slidabl'y mounted in said 'housing and extending out, of one end thereofl toward: said cam surface; roller means carried by said cam engaging elementandl engaging. said cylindrical .camsurface; closure means closing the other end' of' said housing.; and conrpression springs means confined in said housing between said element and said closure meansl for forcing said element into engagement; with said cam surface.

3. In a spring counterbalance for a drafting machine employed on an inclined drawing' boa-rd and including an anchor member secured to. said board and defining a iixedaxis pivotally supporting an arm member of a parallel motion mechanism, the combination of: a cam secured to one of said members and defining a circular cam surface extending about said xed axis and disother oflsaid members definingy atubular housing directed toward said cam surface; a cam engaging element slidably mounted in said housing and extending out of one end thereof to engage said cam surface; means closing the other end of said housing; and compression spring means conned in said housing between said element and said closure means for forcing said element into engagement with said cam surface, said cam and said housing being so positioned that the force of said spring tends to pivotally move said arm member upwardly over said inclined drawing board.'

4. In a spring counterbalance for a drafting machine employed on an inclined drawing board and including an anchor member secured to said board and defining a fixed axis pivotally supporting an arm member of a parallel motion mechanism, the combination of: a cam member carried by said anchor member and defining a circular cam surface extending about said xed axis and disposed eccentrically relative thereto; means on said arm member defining a tubular housing directed toward said cam surface and disposed with its length parallel to the length of said arm member; a cam engaging element slidably mounted in said housing and extending out of one end thereof to engage said cam surface; and coming said cam engaging element into pressure engagement with said cam surface, said cam memyber being so positioned on said anchor member that said cam engaging element is moved by said cam surface to its maximum distance from said fixed axis when said arm member is moved to a position extending downwardly in the direction of inclination of said drawing board.

5. In a spring counterbalance for a drafting machine employed on an inclined drawing board and including an anchor member secured to said board and defining a fixed axis .pivotally supporting an arm member of a parallel motion mechanism, the combination of: a cam member carried by said anchor member and dening a circular cam surface extending about said fixed axis and disposed eccentrically relative thereto; means on said arm member defining a tubular housing directed toward said cam surface and disposed with its length parallel to the length of said arm member; a cam engaging element slidably mounted in said housing and extending out` of one end thereof to engage said cam surface; compression spring means in said housing for urging said cam engaging element into pressure engagement with said cam surface; and means adjustably securing said cam member to said anchor member to permit moving said cam member to different angular positions relative thereto to thereby permit adjustment of the position of said arm member at which said cam engaging element is moved by said cam surface to its maximum distance from said fixed axis.

6. In a spring counterbalance for a drafting machine employed on an inclined drawing board and including an anchor member having an upper board engaging flange clamped against the upper surface of said drawing board and supporting a pivot shaft pivotally supporting an' fining a circular cam surface eccentrically disposed relative to said pivot shaft; a tubular housing formed integrally with said upper board engaging flange and disposed in a position extending the length of said housing toward said cam member; a cam engaging element slidably mounted in said housing and extending out of one end thereof to engage said cam surface; closure means closing the other end of said housing; and compression spring means confined in said housing between said element and said closure means for forcing said element into engagement with said cam surface, said cam and said housing being so positioned that the force of said spring tends to pivotally move said arm member upwardly over said inclined drawing board.

7. In a spring counterbalance for a drafting machine including an anchor member defining a fixed axis pivotally supporting an arm member of a parallel motion mechanism, the combination of a cam secured to one of said members and defining a cam surface; means on the other of said members dening a tubular housing directed toward said cam surface; a cam engaging element slidably mounted in said housing and extending out of one end4 thereof to engage said cam surface; closure means closing the other end of saidhousing; and compression spring means confined in said housing between said element and said closure means for forcing said element into engagement with said cam surface.

8. In a spring counterbalance for a drafting machine including an anchor member dening a xed axis pivotally supporting an arm member of a parallel motion mechanism, the combination of a cam secured to one of said members and defining a cam surface axis; means on the other of said members defining a tubular housing directed toward said cam surface; a cam engaging element slidably mounted in said housing and extending out of one end thereof to engage said cam surface; closure means closing the other end of said housing; and compression spring means confined in said housing between said element and said closure means for forcing said element into engagement with said cam surlface, said closure means being threadedly engaged with said housing whereby rotation of said closure means adjusts the force exerted by said compression spring means.

RUSSELL H. COLE. PERRY F. GLOVER. 

